1. Field of the Invention
The present invention relates to subsea connectors and devices for limiting the bend of flexible pipes or umbilicals used with subsea connections. More particularly, the invention relates to devices used to distribute loads during pull-in operations associated with the bend limiting devices.
2. Description of Related Art
Bend restrictors (or bend limiters) and/or bend stiffeners are used to inhibit overbending of flexible pipes or cable, flowline, and/or umbilical risers where the risers attach to fixed or floating structures such as, but not limited to, subsea riser bases, wellhead connections, pipeline end manifolds (PLEMs), and fixed or floating offshore platforms. The flexible pipes, flowlines, and/or umbilicals may be used, for example, to transport hydrocarbons or other fluids, to and from the surface. As an example, a bend restrictor/limiter may be used to inhibit overbending of an umbilical riser exiting an I-tube or J-tube on an offshore platform.
A bend restrictor/limiter may fit snugly over the riser and be tapered on the outside with a passage on the inside to allow the riser to pass through the bend restrictor/limiter. One end of the bend restrictor/limiter may be coupled to (e.g., secured or attached to) the riser base (e.g., the I-tube or J-tube) while the other end is freely moving. This structure allows the riser to move axially within the bend restrictor/limiter while lateral movement of the riser is inhibited by engaging the inside walls of the bend restrictor/limiter.
The riser may move laterally due to forces such as current or wave action. The stiffness provided by the bend restrictor/limiter limits the curvature of the riser and ensures that the curvature stays within a maximum curvature allowed by the design of the riser. This curvature limitation protects the riser from overbending and/or kinking.
In some subsea operations, the bend restrictor/limiter includes two parts: a guide funnel assembly and a shaft assembly. The guide funnel assembly may be pre-installed on a subsea structure such as an I-tube or J-tube. The shaft assembly may be installed on the riser prior to installation of the riser (e.g., the shaft assembly is installed with the riser at the time of offshore installation).
Typically, a holdback clamp assembly is installed on the riser below the shaft assembly. The holdback clamp assembly prevents the shaft assembly and the bend restrictor/limiter from slipping during pull-in operations (e.g., pull-in of the riser into the guide funnel assembly). The holdback clamp assembly may transfer the pull-in load of the shaft assembly and push the shaft assembly into the guide funnel assembly to engage the assemblies together. The installation loads may be transferred from the holdback clamp assembly into the end of the bend restrictor/limiter and onto the shaft assembly during pull-in operations. In certain cases, the installation loads may be high and the end of the bend restrictor/limiter may be damaged due to the high installation loads (e.g., when there are large angular misalignments between the shaft assembly and the guide funnel assembly during pull-in operations).
System designs using the holdback clamp assembly also require the holdback clamp assembly to be removed by a remotely operated vehicle (ROV) or diver after the shaft assembly is latched into the guide funnel assembly for pull-in operations to continue. Thus, there is a need for a system for a bend restrictor/limiter that better distributes loads in the system to avoid damage to the bend restrictor/limiter during pull-in operations. The system may include an automatic release mechanism to appropriately distribute loads within the shaft assembly and a pull-head during pull-in operations.